How is malignant mesothelioma diagnosed?
Mesothelioma is most often diagnosed after a person goes to a doctor because of symptoms. If there is a reason to suspect you might have mesothelioma, your doctor will use one or more tests to find out. Symptoms might suggest that the problem could be mesothelioma, but tests will be needed to confirm the diagnosis.
Medical history and physical exam
If you have any signs or symptoms that suggest you might have mesothelioma, your doctor will want to take a complete medical history to learn about your symptoms and possible risk factors, especially asbestos exposure. You will also be asked about your general health.
A physical exam can provide information about possible signs of mesothelioma and other health problems. Pleural mesothelioma can cause fluid to build up around the lungs in the chest (called a pleural effusion). In cases of peritoneal mesothelioma, fluid can build up in the abdomen (called ascites). In pericardial mesothelioma, fluid builds up in the sac around the heart (called a pericardial effusion). Rarely, mesothelioma can develop in the groin and look like a hernia. All of these might be found during a physical exam, such as when the doctor listens to these areas with a stethoscope.
If mesothelioma is a possibility, tests will be needed to make sure. These might include imaging tests, blood tests, and other procedures.
Imaging tests use x-rays, radioactive particles, or magnetic fields to create pictures of the inside of your body. Imaging tests may be done for a number of reasons, including to help find a suspicious area that might be cancerous, to learn how far cancer may have spread, and to help determine if treatment has been effective.
This is often the first test done if someone has symptoms such as a constant cough or shortness of breath. It may show an abnormal thickening of the pleura, calcium deposits on the pleura, fluid in the space between the lungs and the chest wall, or changes in the lungs themselves as a result of asbestos exposure. These findings could suggest a mesothelioma.
Computed tomography (CT) scan
The CT scan is an x-ray test that produces detailed cross-sectional images of your body. Instead of taking one picture, like a regular x-ray, a CT scanner takes many pictures as it rotates around you while you are lying on a narrow table. A computer then combines these into images of slices of the body. Unlike a regular x-ray, a CT scan creates detailed images of the soft tissues in the body.
A CT scanner has been described as a large donut, with a narrow table in the middle opening. You will need to lie still on the table while the scan is being done. CT scans take longer than regular x-rays, and you might feel a bit confined by the ring while the pictures are being taken.
CT scans are often used to help look for mesothelioma and to determine the exact location of the cancer. They can also help stage the cancer (determine the extent of its spread). For example, they can show whether the cancer has spread to other organs. This can help to determine if surgery might be a treatment option. Finally, CT scans can be used to learn whether treatment such as chemotherapy has been helpful in shrinking or slowing the growth of the cancer.
Before the test, you might have to drink 1 to 2 pints of a liquid called oral contrast. This helps outline the intestine so that certain areas are not mistaken for tumors. You might also receive an IV (intravenous) line through which a different kind of contrast dye (IV contrast) is injected. This helps better outline structures in your body. The injection can cause some flushing (redness and warm feeling). Some people are allergic and get hives or, rarely, more serious reactions like trouble breathing and low blood pressure. Be sure to tell the doctor if you have any allergies or have ever had a reaction to any contrast material used for x-rays.
This test uses sound waves to look at the heart. It may be done if your doctor suspects that you have fluid around your heart (a pericardial effusion). It can also tell how well the heart is working. For the most common version of this test, you lie on a table while a technician moves an instrument called a transducer over the skin on your chest. A gel is often put on the skin first.
Positron emission tomography (PET) scan
For a PET scan, a radioactive substance (usually a type of sugar related to glucose, known as FDG) is injected into the blood. The amount of radioactivity used is very low. Because cancer cells in the body grow quickly, they absorb more of the sugar than most other cells. After waiting about an hour, you lie on a table in the PET scanner for about 30 minutes while a special camera creates a picture of areas of radioactivity in the body.
The picture from a PET scan is not finely detailed like a CT or MRI scan, but it can provide helpful information about whether abnormal areas seen on these tests are likely to be cancerous or not. For example, it can give the doctor a better idea of whether a thickening of the pleura or peritoneum seen on a CT scan is more likely cancer or merely scar tissue. If you have been diagnosed with cancer, your doctor may use this test to see if the cancer has spread to lymph nodes or other parts of the body. A PET scan can also be useful if your doctor thinks the cancer may have spread but doesn't know where.
Some machines can do both a PET and CT scan at the same time (PET/CT scan). This lets the doctor compare areas of higher radioactivity on the PET scan with the more detailed appearance of that area on the CT.
Magnetic resonance imaging (MRI) scan
Like CT scans, MRI scans make detailed images of soft tissues in the body. But MRI scans use radio waves and strong magnets instead of x-rays. The energy from the radio waves is absorbed and then released in a pattern formed by the type of body tissue and by certain diseases. A computer translates the pattern into very detailed images of parts of the body. A contrast material called gadolinium is often injected into a vein before the scan to better show details. This contrast is different than the one used for CT scans, so being allergic to one doesn’t mean you are allergic to the other.
MRI scans can sometimes help show the exact location and extent of a tumor since they provide very detailed images of soft tissues. For mesotheliomas, they may be useful in looking at the diaphragm (the thin band of muscle below the lungs that helps us breathe), a possible site of cancer spread.
MRI scans take longer than CT scans – often up to an hour. You may have to lie inside a narrow tube, which can upset people with a fear of enclosed spaces. Special, more open MRI machines may be an option in some cases. The MRI machine makes buzzing and clicking noises that you might find disturbing. Some places will give you earplugs to help block this out.
More information on radiation therapy can be found in the Radiation section of our website, or in our document Understanding Radiation Therapy: A Guide for Patients and Families
Blood levels of certain substances are often higher in people with mesothelioma:
- Soluble mesothelin-related peptides (SMRPs), detected with the MesoMark® test
Blood tests for these substances are not used to diagnose mesothelioma, but high levels may make the diagnosis more likely.
If you have been diagnosed with mesothelioma, other blood tests will be done to check your blood cell counts and levels of certain chemicals in the blood. These tests can give the doctor an idea of how extensive the disease may be, and how well organs such as the liver and kidneys are working.
Tests of fluid and tissue samples
Symptoms and test results may strongly suggest that a person has mesothelioma, but the actual diagnosis is made by removing cells from an abnormal area and looking at them under a microscope. This is known as a biopsy. It may be done in different ways, depending on the situation.
Removing fluid for testing
If mesothelioma might be causing a buildup of fluid in the body, a sample of this fluid can be removed by inserting a thin, hollow needle through the skin and into the fluid to remove it. Numbing medicine is used on the skin before the needle is inserted. This may be done in a doctor's office or in the hospital. Sometimes ultrasound (or an echocardiogram) is used to guide the needle (these use sound waves to take pictures of parts of the body).
This procedure has different names depending on where the fluid is:
- Thoracentesis removes fluid from the chest.
- Paracentesis removes fluid from the abdomen.
- Pericardiocentesis removes fluid from the sac around the heart.
The fluid is then tested to check its chemical makeup and is looked at under a microscope to see if it contains cancer cells. If cancer cells are found, special tests might be able to tell whether the cancer is a mesothelioma, a lung cancer, or another type of cancer.
Even if no cancer cells are found in the fluid, cancer may still be present. In many cases, doctors need to get an actual sample of the mesothelium (the pleura, peritoneum, or pericardium) to determine if a person has mesothelioma.
Suspected tumors in the chest are sometimes sampled by needle biopsy. A long, hollow needle is passed through the skin in the chest between the ribs and into the pleura. Imaging tests such as CT scans are used to guide the needle into the tumor so that small samples can be removed to be looked at under the microscope. This is often done using just numbing medicine.
Needle biopsy can also be used to get samples of the lymph nodes in the space between the lungs to see if the cancer has spread there (see “Endobronchial ultrasound needle biopsy”).
Needle biopsies do not require a surgical incision or overnight hospital stay. But the downside is that sometimes the samples removed are not big enough to make an accurate diagnosis. This is especially true for mesothelioma. A more invasive biopsy method may be needed.
There is a slight chance that the needle could put a small hole in the lung during the biopsy. This can cause air to build up in the space between the lung and the chest wall (known as a pneumothorax). A small pneumothorax may cause no symptoms. It may only be seen on an x-ray done after the biopsy, and it will often go away on its own. But a larger pneumothorax can make part of a lung collapse and might need to be treated. The treatment is placement of a small tube (a catheter) through the skin and into the space between the lungs. The tube is used to suck the air out in order to re-expand the lung and is left in place for a short time.
An endoscope is a thin, tube-like instrument used to look inside the body. It has a light and a lens (or tiny video camera) on the end for viewing and often has a tool to remove tissue samples. Endoscopes have different names depending on the part of the body where they’re used. Endoscopic biopsy is commonly used to diagnose mesothelioma.
Thoracoscopy: This procedure uses an endoscope called a thoracoscope to look at areas inside the chest. It can be used to look at the pleura and take tissue samples for biopsies. Thoracoscopy is done in the operating room while you are under general anesthesia (in a deep sleep). The doctor inserts the thoracoscope through one or more small cuts made in the chest wall to look at the space between the lungs and the chest wall. This lets the doctor see possible areas of cancer and remove small pieces of tissue to look at under the microscope. The doctor can also sample lymph nodes and fluid and see if a tumor is growing into nearby tissues or organs. Thoracoscopy can also be used as part of a procedure to keep fluid from building up in the chest. This is called pleurodesis and is discussed in the section “Palliative procedures used for malignant mesothelioma.”
Laparoscopy: For this test, the doctor uses an endoscope called a laparoscope to look inside the abdomen and biopsy any peritoneal tumors. This is done in the operating room while you are under general anesthesia (in a deep sleep). The laparoscope is inserted into the abdomen through small cuts on the front of the abdomen.
Mediastinoscopy: If imaging tests such as a CT scan suggest that the cancer has spread to the lymph nodes between the lungs, the doctor may want to remove some of them to see if they really contain cancer. This area is the mediastinum, and looking at it with an endoscope is called mediastinoscopy. This is also done in an operating room while you are under general anesthesia (in a deep sleep).
A small cut is made in the front of the neck above the breastbone (sternum) and a thin, hollow, lighted tube (called a mediastinoscope) is inserted behind the sternum. Special instruments can be passed through this tube to take tissue samples from the lymph nodes along the windpipe and the major bronchial tube areas.
Cancers in the lung often spread to lymph nodes, but mesotheliomas do this less often. Testing the lymph nodes can help show whether a cancer is still localized or if it has started to spread, which might affect treatment options. It can also sometimes help distinguish lung cancer from mesothelioma.
Bronchoscopy: This test does not require any cuts in the skin. It uses a bronchoscope – a long, thin, flexible, fiber-optic tube that is placed down the throat and into the lungs to look at the lining of the main airways. This procedure is done while you are asleep or sedated. If a tumor is found, the doctor can take a small sample of the tumor through the tube.
Patients with mesothelioma don’t need to have bronchoscopy to see if tumors are in their airways (because that isn’t where tumors from mesothelioma are found). Instead, bronchoscopy may be used to biopsy lymph nodes near the lungs (instead of using mediastinoscopy). This procedure is called endobronchial ultrasound needle biopsy. For this, a bronchoscope with an ultrasound device at its tip is passed down into the windpipe. The ultrasound device uses sound waves to let the doctor see the nearby lymph nodes. A hollow needle is then passed down the bronchoscope and through the airway wall into the nodes to take biopsy samples. This procedure may be done with either general anesthesia (you are asleep), or with numbing medicine (local anesthesia) and light sedation.
Open surgical biopsy
Sometimes, endoscopic biopsies aren’t enough to make a diagnosis and more invasive procedures are needed. By making an incision in the chest (thoracotomy) or an incision in the abdomen (laparotomy) the surgeon can remove a larger sample of tumor or, sometimes, remove the entire tumor.
Testing the samples in the lab
No matter how they were obtained, all biopsy and fluid samples are sent to the pathology lab. There, a doctor will look at them under a microscope and test them to find out if they contain cancer cells (and if so, what type of cancer it is).
It is often hard to diagnose mesothelioma by looking at cells from fluid around the lungs, abdomen, or heart. It can even be hard to diagnose mesothelioma with tissue from small needle biopsies. Under the microscope, mesothelioma can often look like other types of cancer. For example, pleural mesothelioma may resemble some types of lung cancer, and peritoneal mesothelioma in women may look like some cancers of the ovaries.
For this reason, special lab tests are often done to help tell mesothelioma from some other cancers.
Immunohistochemistry: This test looks for different proteins on the surface of the cells or inside them. It can be used to tell if the cancer is a mesothelioma or a lung cancer, which can sometimes appear to start in the inner lining of the chest.
DNA microarray analysis: This is a newer test that actually looks at patterns of genes in the cancer cells. Mesothelioma cells have different gene patterns than other cancer cells.
Electron microscopy: This can sometimes help diagnose mesothelioma. The electron microscope can magnify samples many more times than a normal light microscope. This more powerful microscope makes it possible to see the small parts of the cancer cells that can distinguish mesothelioma from other types of cancer.
For more about these and other tests that are done on tissue samples, you can read our document Testing Biopsy and Cytology Specimens for Cancer.
If mesothelioma is diagnosed, the doctor will also determine what type of mesothelioma it is, based on the patterns of cells seen in the microscope. Most mesotheliomas are classified as either epithelioid, sarcomatoid, or mixed/biphasic.
Pulmonary function tests
If mesothelioma has been diagnosed, pulmonary function tests (PFTs) may be done to see how well your lungs are working. This is especially important if surgery may be an option to treat the cancer. Surgery often requires removing part or all of a lung, so it’s important to know how well the lungs are working to start with. These tests can give the surgeon an idea of whether surgery may be an option, and if so, how much lung can safely be removed.
There are a few different types of PFTs, but they all basically have you breathe in and out through a tube that is connected to a machine that measures your lung function.
Last Medical Review: 12/19/2013
Last Revised: 12/19/2013